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Upwelling System (upwelling + system)
Kinds of Upwelling System Selected AbstractsFacies development, depositional settings and sequence stratigraphy across the Ordovician,Silurian boundary: a new perspective from the Barrandian area of the Czech RepublicGEOLOGICAL JOURNAL, Issue 2 2006torch Abstract The Hirnantian and Llandovery sedimentary succession of the Barrandian area has been assigned to middle and outer clastic-shelf depositional settings, respectively. Deposition was influenced by the remote Gondwanan glaciation and subsequent, long-persisting, post-glacial anoxia triggered by a current-driven upwelling system. High-resolution graptolite stratigraphy, based upon 19 formally defined biozones,largely interval zones,and five subzones, enabled a detailed correlation between 42 surface sections and boreholes, and enabled linking of the sedimentary record, graptoloid fauna dynamics, organic-content fluctuations and spectral gamma-ray curves. The Hirnantian and Llandovery succession has been subdivided into four biostratigraphically dated third-order sequences (units 1,4). Time,spatial facies distribution recorded early and late Hirnantian glacio-eustatic sea-level lowstands separated by a remarkable mid-Hirnantian rise in sea-level. A major part of the post-glacial sea-level rise took place within the late Hirnantian. The highstand of Unit 2 is apparently at the base of the Silurian succession. Short-term relative sea-level drawdown and a third-order sequence boundary followed in the early Rhuddanian upper acuminatus Zone. Early Aeronian and late Telychian sea-level highstands and late Aeronian drawdown of likely eustatic origin belong to units 3 and 4. Sea-level rise culminated in the late Telychian, which may also be considered as a highstand episode of a second-order Hirnantian,early Silurian cycle. Facies and sequence-stratigraphic analysis supports recent interpretations on nappe structures in the core part of the Ordovician,Middle Devonian Prague Synform of the Barrandian. Copyright © 2006 John Wiley & Sons, Ltd. [source] Hierarchical Bayesian modelling of wind and sea surface temperature from the Portuguese coastINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 9 2010Ricardo T. Lemos Abstract In this work, we revisit a recent analysis that pointed to an overall relaxation of the Portuguese coastal upwelling system, between 1941 and 2000, and apply more elaborate statistical techniques to assess that evidence. Our goal is to fit a model for environmental variables that accommodate seasonal cycles, long-term trends, short-term fluctuations with some degree of autocorrelation, and cross-correlations between measuring sites and variables. Reference cell coding is used to investigate similarities in behaviour among sites. Parameter estimation is performed in a single modelling step, thereby producing more reliable credibility intervals than previous studies. This is of special importance in the assessment of trend significance. We employ a Bayesian approach with a purposely developed Markov chain Monte Carlo method to explore the posterior distribution of the parameters. Our results substantiate most previous findings and provide new insight on the relationship between wind and sea surface temperature off the Portuguese coast. Copyright © 2009 Royal Meteorological Society [source] Late Quaternary upwelling off tropical NW Africa: new micropalaeontological evidence from ODP Hole 658C,JOURNAL OF QUATERNARY SCIENCE, Issue 3 2006Simon K. Haslett Abstract Planktonic foraminifera and radiolaria have been analysed in a Late Quaternary (40,0,ka) sediment sequence from Ocean Drilling Program (ODP) Hole 658C located under a coastal upwelling system near Cap Blanc, offshore northwest Africa, in order to document the palaeoceanographic history of the area. Temporal variations in species abundance and faunal assemblage analysis reveal a tripartite phased sequence of palaeoceanographic change through the Late Quaternary. Phase 1 spans 40,14.5,ka and is characterised by moderate upwelling, but Heinrich event 2 is distinguished as a brief episode of strengthened upwelling. Phase 2 begins with a change in a number of variables at ca. 14.5,ka and extends to ca. 5.5,ka. This phase is characterised by a general strengthening of upwelling, but may be subdivided into three minor phases including (a) the recognition of the Younger Dryas, marked by a temporary reduction in upwelling strength, followed by (b) an intensification of upwelling, and (c) upwelling and high productivity between 8 and 5.5,ka. This phase of upwelling corresponds with maximum Holocene cooling, possibly triggered by the collapse of the Laurentide ice sheet. Phase 3 extends from 5.5 to 0,ka and is characterised by weak upwelling and significant calcite dissolution. These phases are related to climatic events, particularly the African Humid Period (AHP), which is coincident with Phase 2. The AHP is characterised by increased precipitation, linked to an intensification of the African monsoon that enhances North East Trade Wind-driven coastal upwelling and is associated with the expansion of continental vegetation across North Africa. Copyright © 2006 John Wiley & Sons, Ltd. [source] Biogeography of common dolphins (genus Delphinus) in the Southwestern Atlantic OceanMAMMAL REVIEW, Issue 1 2010Maurício TAVARES ABSTRACT 1The common dolphins (genus Delphinus) have one of most problematic taxonomies and complex distribution patterns of all cetaceans. Although the taxonomy and the distribution seem to have been clarified somewhat in the eastern North Pacific and Indo-Pacific Oceans, many questions remain in the Southwestern Atlantic Ocean (SWA). We review the biogeography of Delphinus in the SWA. 2We reviewed data from strandings, incidental catches and sightings since 1922. Systematic surveys were conducted in five major areas. Twenty-one natural history collections were examined, and 135 skulls were measured. 3A total of 184 records of common dolphins were compiled. Delphinus apparently occurs in three stocks in the SWA: one located in northern Brazil and two from southeastern Brazil (,22°S) to central Argentina (,42°S). Two distinct patterns in habitat use were observed by depth: in southeastern Brazil, sightings were restricted to coastal waters with water depths ranging from 18m to 70m. On the other hand, in the area that extends from southern Brazil to Central Argentina (from 28°S to 42°S), sightings were recorded in deeper waters, ranging from 71m to 1435m, with the exception of occasional coastal sightings. The cranial analyses demonstrated that both short-beaked common dolphins Delphinus delphis and long-beaked common dolphins Dephinus capensis occur in the SWA. 4In the SWA, Delphinus seems to occur near areas of high productivity. One stock is associated with the productive waters discharged by the Amazon River and possibily with the coastal upwelling system off the coast of Venezuela, while the other stocks are associated with the Cabo Frio upwelling system and the Subtropical Convergence. Our results indicate that the current taxonomy does not adequately reflect the amount of variation within the genus in the world. [source] Simulation and quantification of enrichment and retention processes in the southern Benguela upwelling ecosystemFISHERIES OCEANOGRAPHY, Issue 5 2006CHRISTOPHE LETT Abstract Important environmental processes for the survival and recruitment of early life stages of pelagic fishes have been synthesized through Bakun's fundamental triad as enrichment, concentration and retention processes (A. Bakun, 1996, Patterns in the Ocean. Ocean Processes and Marine Population Dynamics. San Diego, CA, USA: University of California Sea Grant). This conceptual framework states that from favourable spawning habitats, eggs and larvae would be transported to and/or retained in places where food originating from enrichment areas would be concentrated. We propose a method for quantifying two of the triad processes, enrichment and retention, based on the Lagrangian tracking of particles transported within water velocity fields generated by a three-dimensional hydrodynamic model. We apply this method to the southern Benguela upwelling ecosystem, constructing putative maps of enrichment and retention. We comment on these maps regarding main features of the circulation in the region, and investigate seasonal variability of the processes. We finally discuss the results in relation to available knowledge on the reproductive strategies of two pelagic clupeoid species abundant in the southern Benguela, anchovy (Engraulis encrasicolus) and sardine (Sardinops sagax). Our approach is intended to be sufficiently generic so as to allow its application to other upwelling systems. [source] Predicting population consequences of ocean climate change for an ecosystem sentinel, the seabird Cassin's aukletGLOBAL CHANGE BIOLOGY, Issue 7 2010SHAYE G. WOLF Abstract Forecasting the ecological effects of climate change on marine species is critical for informing greenhouse gas mitigation targets and developing marine conservation strategies that remain effective and increase species' resilience under changing climate conditions. Highly productive coastal upwelling systems are predicted to experience substantial effects from climate change, making them priorities for ecological forecasting. We used a population modeling approach to examine the consequences of ocean climate change in the California Current upwelling ecosystem on the population growth rate of the planktivorous seabird Cassin's auklet (Ptychoramphus aleuticus), a demographically sensitive indicator of marine climate change. We use future climate projections for sea surface temperature and upwelling intensity from a regional climate model to forecast changes in the population growth rate of the auklet population at the important Farallon Island colony in central California. Our study projected that the auklet population growth rate will experience an absolute decline of 11,45% by the end of the century, placing this population on a trajectory toward extinction. In addition, future changes in upwelling intensity and timing of peak upwelling are likely to vary across auklet foraging regions in the California Current Ecosystem (CCE), producing a mosaic of climate conditions and ecological impacts across the auklet range. Overall, the Farallon Island Cassin's auklet population has been declining during recent decades, and ocean climate change in this century under a mid-level emissions scenario is projected to accelerate this decline, leading toward population extinction. Because our study species has proven to be a sensitive indicator of oceanographic conditions in the CCE and a powerful predictor of the abundance of other important predators (i.e. salmon), the significant impacts we predicted for the Cassin's auklet provide insights into the consequences that ocean climate change may have for other plankton predators in this system. [source] | |||||||||||||